Abstract: Using ab initio molecular orbital theory,the hydrogen abstraction reaction CH2O＋O[3P]→CHO＋OH has been studied.The geometries of the reactants,transition state and products have been optimized at the QCISD/6311G[d,p] level.The forward and reverse reaction potential barriers are 38.86 kJ•mol－1 and 67.23 kJ•mol－1 respectively at the QCISD(t,full)/6311G[d,p]//QCISD/6311G[d,p].By analyzing the changes of the generalized normalmode vibrational frequencies along the IRC,we found that the C－H bond breaking and the O－H bond forming took place as a concerted process.And there is a reactive vibrational normalmode which leads to the process of reaction from reactants to products.At the temperature range of 1 300～2 270 K,the forward and reverse reaction rate constants obtained by using the improved canonical variational transition state theory (ICVT),are consistent with the experimental values.

Key words: Formaldehyde, O[³P], Rate constant, Ab initio